Method and Its Apparatus for Inspecting Defects

ABSTRACT

A defect inspection apparatus is capable of inspecting an extremely small defect present on the top and edge surfaces of a sample such as a semiconductor substrate or a thin film substrate with high sensitivity and at high speed. The defect inspection apparatus has an illumination optical system, a plurality of detection optical units and a signal processor. One or more of the detection optical units receives either light diffracted from an edge portion of the sample or light diffracted from an edge grip holding the sample. The one or more of the detection optical units shields the diffracted light received by the detection optical unit based on a signal obtained by monitoring an intensity of the diffracted light received by the detection optical unit in order to inspect a sample portion located near the edge portion and a sample portion located near the edge grip.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for inspecting adefect present on the top and edge surfaces of a sample such as asemiconductor substrate and a thin film substrate with high sensitivityand at high speed.

In a production line for a semiconductor substrate or for a thin filmsubstrate, an inspection operation is performed to inspect a defect onthe surface of the semiconductor substrate or on the surface of the thinfilm substrate in order to maintain or improve the yield of products.

As a conventional method and apparatus for inspecting a defect,JP-A-H09-304289 (Patent Document 1), JP-A-2003-240730 (Patent Document2) and JP-A-2008-32621 (Patent Document 3) are known.

Patent Document 1 discloses an apparatus for inspecting the surface of awafer. The apparatus described in Patent Document 1 has a low-angleoptical receiver and a high-angle optical receiver. The low-angleoptical receiver is located such that it forms an elevation angle of 30degrees or less with respect to the surface of the wafer, while thehigh-angle optical receiver is located such that it forms an elevationangle of more than 30 degrees with respect to the surface of the wafer.The apparatus uses a laser beam to scan the wafer. Each of the low-angleand high angle optical receivers receives light scattered from the waferilluminated with the laser beam to detect a foreign material by means ofthe scanning. The foreign material detected from a certain area of thewafer by only the high-angle optical receiver is treated as a crystaldefect, while the foreign material detected from the certain area of thewafer by the low-angle optical receiver is treated as an attachedforeign material.

Patent Document 2 discloses an apparatus for inspecting the surface of awafer. The apparatus described in Patent Document 2 has a detector.Light scattered from an edge portion of the wafer has high directivityand is distributed in a direction extending from the edge portion andparallel to a normal to the surface of the wafer. Light scattered from adefect (such as a foreign material) present on the edge portion of thewafer does not exhibit high directivity. A detector(s) detects the lightscattered from the defect under the condition that one or more detectionoptical units are arranged in a direction(s) other than the directionextending from the edge portion and parallel to the normal to thesurface of the wafer and do not receive the light scattered from theedge portion. Alternatively, the detector(s) detects the light scatteredfrom the defect, while a space filter(s) arranged on a Fourier transformsurface(s) of the one or more detection optical units shields the lightscattered from the edge portion.

Patent Document 3 discloses an apparatus for inspecting the surface ofan object that is to be inspected. The apparatus described in PatentDocument 3 irradiates and scans the surface of the object with a lightbeam to detect light scattered from the object. The apparatus has aposition detection unit for detecting the relative position of theobject to the position of a spot of the light beam. The apparatus alsoincludes one of the following: a light shielding unit for preventing thescattered light from being incident on a detector for detecting thescattered light before the spot of the light beam detected by theposition detection unit reaches an edge portion of the object; anoptical path shielding mechanism for shielding the light beam on anoptical path of the light beam before the spot of the light beamdetected by the position detection unit reaches the edge portion of theobject; and a controller for stopping a function of the detector fordetecting the scattered light before the spot of the light beam detectedby the position detection unit reaches the edge portion of the object.The apparatus reduces degradation of the detector due to the scatteredlight. In addition, Patent Document 3 describes that when the light beamreaches the edge portion of the object, the apparatus scans the objectwith the light beam to prevent an increase in the amount of the lightscattered toward the detector from the edge portion.

In a process for manufacturing a semiconductor substrate or the like, aportion of the substrate, which is located near an outer circumferentialedge portion (hereinafter referred to as an edge portion) of thesubstrate, may easily have a defect such as peeling. It is, therefore,necessary to inspect the defect present on the edge portion of thesubstrate and deal with the defect present on the edge portion early orin advance. A challenge is to maximize the total area of a chip(s) thatis included in the total area of the substrate and can be used as a goodproduct(s) and thereby to improve the yield of the product(s).

However, the defect inspection on the edge portion is not taken intoaccount in Patent Document 1.

The apparatus described in Patent Document 2 may have a detectionoptical unit that does not receive light having high directivity anddiffracted from the edge portion. Alternatively, the apparatus describedin Patent Document 2 may be configured with the space filter thatshields the light diffracted from the edge portion and having highdirectivity to prevent the detector from detecting the diffracted light.The apparatus described in Patent Document 3 prevents the scatteredlight (diffracted light) from being incident on the detector fordetecting the scattered light, or shields the light beam on the opticalpath, or stops the function of the detector for detecting the scatteredlight, before the spot of the light beam detected by the positiondetection unit reaches the edge portion of the object. This prevents thelight scattered (diffracted) from the edge portion from being detected.

However, Patent Documents 2 and 3 do not sufficiently take into accountthe inspection of a substrate portion located near the edge portion ofthe substrate at high speed and with high sensitivity.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for inspecting aminute defect present on the top and edge surfaces of a substrate suchas a semiconductor substrate and a thin film substrate with highsensitivity and at high speed.

According to the present invention, an apparatus for inspecting a defectincludes: an illumination optical system for guiding light emitted by alight source onto a sample to illuminate a particular area of the sampleas an illumination area;

a plurality of detection optical units for converging from a pluralityof directions light generated from the sample when illuminated by theillumination optical system to obtain detection signals of the light ona direction-by-direction basis; and

a signal processor for processing a plurality of detection signalsobtained by the plurality of detection optical units to judge whether ornot a defect is present on the sample;

wherein upon inspection of a near-edge portion of the sample, in adetection optical unit, of the plurality of detection optical units, onwhich diffracted light generated from the near edge portion is incident,the incident diffracted light is blocked (shielded) by diffracted lightblocking means (diffracted light shielding means) in accordance with asignal obtained by monitoring the intensity of the incident diffractedlight.

According to the present invention, an apparatus for inspecting a defectincludes: an illumination optical system for guiding light emitted by alight source onto a sample to illuminate a particular area of the sampleas an illumination area;

a plurality of detection optical units for converging from a pluralityof directions light generated from the sample when illuminated by theillumination optical system to obtain detection signals of the light ona direction-by-direction basis; and

a signal processor for processing a plurality of detection signalsobtained by the plurality of detection optical units to judge whether ornot a defect is present on the sample;

wherein upon inspection of a near edge grip portion of the sample, in adetection optical unit, of the plurality of detection optical units, onwhich diffracted light generated from an edge grip portion is incident,the incident diffracted light is blocked (shielded) by diffracted lightblocking means (diffracted light shielding means) in accordance with asignal obtained by monitoring the intensity of the incident diffractedlight.

According to the present invention, an apparatus for inspecting a defectincludes: an illumination optical system for guiding light emitted by alight source onto a sample to illuminate a particular area of the sampleas an illumination area;

a plurality of detection optical units for converging from a pluralityof directions light generated from the sample when illuminated by theillumination optical system to obtain detection signals of the light ona direction-by-direction basis; and

a signal processor for processing a plurality of detection signalsobtained by the plurality of detection optical units to judge whether ornot a defect is present on the sample;

wherein upon inspection of a near edge portion and a near edge gripportion of the sample, in a detection optical unit, of the plurality ofdetection optical units, on which is incident either diffracted lightgenerated from the near edge portion or diffracted light generated froman edge grip portion, the diffracted light incident on the detectionoptical unit is blocked by diffracted light blocking means in accordancewith a signal obtained by monitoring the intensity of the incidentdiffracted light.

According to the present invention, an apparatus for inspecting a defectincludes: an illumination optical system for guiding light emitted by alight source onto a sample to illuminate a particular area of the samplewith polarized light;

a plurality of detection optical units for converging from a pluralityof directions light generated from the sample when illuminated with thepolarized light by the illumination optical system to obtain detectionsignals of the light on a direction-by-direction basis; and

a signal processor for processing a plurality of detection signalsobtained by the plurality of detection optical units to judge whether ornot a defect is present on the sample;

wherein upon inspection of a near edge portion and a near edge gripportion of the sample, in a detection optical unit, of the plurality ofdetection optical units, on which is incident either diffracted lightgenerated from the near edge portion or diffracted light generated froman edge grip portion, the polarization components of the diffractedlight incident on the detection optical unit are blocked by a polarizingfilter.

According to the present invention, the edge grip holding the sample hasroughness (on the top and edge surfaces thereof) small enough to ensurethat light scattered from the edge grip has a smaller intensity thanthat of light scattered from a defect present on the sample or that thelight detectors are not saturated by light. In addition, the edge griphas a three-dimensional shape to prevent light diffracted from the edgegrip from being incident on a main light detector.

According to the present invention, a portion of the sample, which islocated near the edge portion of the sample, can be inspected with highsensitivity in a similar manner to inspection of a top surface of thesample.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of apreferred embodiment of the invention, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the outline configuration of a defectinspection apparatus according to an embodiment of the presentinvention.

FIG. 2A is a plan view of a wafer and shows the shape of an ellipticalillumination area having a long length in a certain direction and ashort length in a direction perpendicular to the certain direction.

FIG. 2B is a diagram showing a spiral trajectory of the illuminationarea on the wafer by a rotational movement of a rotary stage and atranslational movement of a stage.

FIG. 3 is a diagram showing the outline configuration of each detectionoptical unit.

FIG. 4A is a diagram showing an angular range in which detection opticalunits detect scattered light.

FIG. 4B1 is a schematic diagram showing the case where four low-angledetection optical units and four high-angle detection optical units arearranged.

FIG. 4B2 is a diagram showing the case where four low-angle detectionoptical units and one high-angle detection optical unit are arranged.

FIG. 5A is a diagram showing the configuration of part of anillumination optical system in the case where a transparent opticalelement is used as an illumination intensity distribution controlelement.

FIG. 5B is a diagram showing the configuration of part of theillumination optical system in the case where a reflective opticalelement is used as the illumination intensity distribution controlelement.

FIG. 5C is a plan view of the illumination intensity distributioncontrol element having a function for two-dimensionally changing theintensity or phase of light passing through the optical element in asurface of the optical element that is perpendicular to an optical axisof the optical element.

FIG. 5D is a plan view of the illumination intensity distributioncontrol element having a function for one-dimensionally changing theintensity or phase of light passing through the optical element in thesurface of the optical element that is perpendicular to the optical axisof the optical element.

FIG. 5E is a perspective view of the illumination intensity distributioncontrol element having an inner surface coated by reflective coating andexhibiting a fixed transmittance distribution or a fixed phasedistribution.

FIG. 6A is a graph showing an illumination intensity distribution of alaser beam emitted by a laser source, the illumination intensitydistribution being represented by substantial Gaussian distribution.

FIG. 6B is a graph showing a uniform illumination intensity distributionof a laser beam emitted by the laser source.

FIG. 6C is a graph showing an illumination intensity distribution of alaser beam emitted by the laser source, the illumination intensitydistribution dropped an intensity of a central portion compared with theuniform illumination intensity distribution shown in FIG. 6B.

FIG. 7 is a block diagram showing an analog processor included in asignal processor.

FIG. 8 is a block diagram showing a digital processor included in thesignal processor.

FIG. 9A is a plan view of the wafer and shows an illumination arealocated near an edge portion of the wafer by scanning in a direction S1and a direction S2.

FIG. 9B is a cross sectional view of the wafer in the case where theillumination area is located near the edge portion of the wafer.

FIG. 9C is a plan view of the wafer and shows light diffracted from theedge portion of the wafer and light scattered from the edge portion ofthe wafer.

FIG. 10A is a plan view of detection optical units in the case there thelight diffracted from the edge portion is incident on some of thedetection optical units.

FIG. 10B is a graph showing the relationship between the position (of aportion of the wafer) in a radial direction of the wafer and a signalindicating the intensity of the light diffracted from the edge portionin the case where a distribution of intensities of illumination light isrepresented by a Gaussian distribution.

FIG. 10C is a graph showing the relationship between the position (of aportion of the wafer) in the radial direction of the wafer and a signalindicating the intensity of the light diffracted from the edge portionin the case where a distribution of intensities of illumination light isuniform.

FIG. 11 is a diagram showing the configuration of a light shielding unitthat is adapted to shield the light diffracted from the edge portion andincluded in a detection optical unit that receives the light diffractedfrom the edge portion.

FIG. 12A is a cross sectional view and plan view of the wafer and anedge grip that holds the wafer.

FIG. 12B is a plan view of the wafer and shows light diffracted from theedge grip.

FIG. 12C is a plan view of detection optical units in the case where adistance k is selected to be a value k1 that minimizes the number of thedetection optical units receiving the light diffracted from the edgegrip.

FIG. 12D is a plan view of the detection optical units in the case wherethe distance k is selected to be a value k2 that results in the factthat the light diffracted from the edge grip is not incident on any ofthe detection optical units.

FIG. 13A is a plan view of the detection optical units and showspolarization states of light diffracted from the edge portion and theedge grip in the case where illumination is performed with a P-polarizedlaser beam.

FIG. 13B is a plan view of the detection optical units and showspolarization states of light diffracted from the edge portion and theedge grip in the case where illumination is performed with anS-polarized laser beam.

FIG. 14 is a diagram showing the configuration of a unit (wafer crosssectional profile measurement unit) for measuring displacement of theillumination area.

FIG. 15 is a diagram showing the configuration of a unit for correctingthe position of the illumination area.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates the configuration of a defect inspection apparatusaccording to an embodiment of the present invention. The defectinspection apparatus includes an illumination optical system 101;detection optical units 102 a and 102 b; a stage 103 capable of mountinga wafer 1 thereon; a signal processor 105; an overall control unit 53;and a display unit 54.

The illumination optical system 101 includes a laser source 2, anattenuator 3, a polarizing element 4, a beam expander 7, an illuminationintensity distribution control element 5, reflective mirrors m1 and m2,and a focusing lens 6. The laser source 2 emits a laser beam. Theattenuator 3 adjusts the emitted laser beam to a given intensity. Thepolarizing element 4 then adjusts the intensity-adjusted laser beam to apolarized state desired. The beam expander 7 adjusts the resultant laserbeam to a given beam diameter. The diameter-adjusted laser beam is thendirected by the reflective mirrors and the focusing lens 6 onto a spoton the wafer 1 to be inspected. The illumination intensity distributioncontrol element 5 is used to control the distribution of illuminationintensity across the wafer 1. As shown in FIG. 1, the illuminationoptical system 101 is configured to illuminate the wafer 1 with a laserbeam at an oblique incident angle, meaning that the incident laser beamis oblique to a normal to the surface of the wafer 1. However, theillumination optical system 101 is also capable of illuminating thewafer 1 with a laser beam at the perpendicular incident angle by way ofanother optical path not shown in FIG. 1. The incident angle of a laserbeam can thus be changed according to wafer areas to be inspected.

Used as the laser source 2 upon detection of micro-scale defects presentin upper layers of the wafer 1 including its uppermost layer is one thatoscillates a short-wavelength ultraviolet or vacuum ultraviolet laserbeam and is powerful enough to output such a laser beam of 1 watt orhigher. To detect defects located further down from the upper layers,one that oscillates a visible or infrared laser beam is used as thelaser beam 2.

The stage 103 has a stage controller 55, a translation stage 11, arotary stage 10, and a Z stage (not shown). FIG. 2 show the relationshipbetween an illumination area 20 on the wafer 1 and a beam scanningdirection (illumination-area moving direction) defined by a rotationalmovement of the rotary stage 10 and by a translational movement of thetranslation stage 11 and the resultant trace T of the illumination areaacross the wafer 1. As shown in FIG. 2A, the illumination area 20 iselliptical in shape, being long in one direction and short in thedirection perpendicular to that direction. This shape is formed byillumination intensity distribution control or by oblique illuminationby means of the illumination optical system 101. The rotational movementof the rotary stage 10 moves the illumination area 20 in acircumferential direction S1 of a circle that has as its center therotational axis of the rotary stage 10. In addition, the translationalmovement of the translation stage 11 moves the illumination area 20 in atranslational direction S2 of the translation stage 11. The illuminationoptical system 101 is configured such that the longitudinal direction ofthe illumination area 20 is parallel to the direction S2 and such thatthe illumination area 20 passes through the rotational axis of therotary stage 10 by beam scanning in the direction S2. The Z stage movesin a height direction of the wafer 1, that is, in an extending directionof a normal to the surface of the wafer 1. The translation stage 11 isdesigned to move in the direction S2 by a distance equal to or smallerthan the longitudinal-direction length of the illumination area 20during a 360-degree rotation of the rotary stage 10. Such movements ofthe two stages during beam scanning result in the spiral trace T of theillumination area 20, whereby the laser beam is scanned across theentire surface of the wafer 1.

The detection optical unit 102 a and 102 b are each configured toconverge and detect scattered or diffracted lights, but the lightsdetected differ in direction and angle between those detected by thedetection optical unit 102 a and those detected by the detection opticalunit 102 b. FIG. 3 shows the configuration of the detection optical unit102 a. Because the detection optical unit 102 b is structurally the sameas the detection optical unit 102 a, it is not discussed herein. Asdescribed later with reference to FIGS. 4B1 and 4B2, the defectinspection apparatus according to the present embodiment includes otherdetection optical units (not shown in FIG. 1) which are mutuallydifferent in addition to the detection optical unit 102 a and 102 b forthe purpose of detecting scattering lights having a wide scatter angularrange.

The detection optical unit 102 a includes an imaging lens 8, apolarizing filter 13, and a light detector 9. The polarizing filter 13can be moved into or out of the optical axis A of the imaging lens 8 andcan be rotated to change the direction of light detection. Thepolarizing filter 13 is used to reduce scattered-light components due towafer roughness and diffracted- or scattered-light components due to theedge of the wafer, both attributable to noise.

The illumination area 20 is focused onto the light detector 9 by theimaging lens 8. To achieve detection of low-intensity lights scatteredfrom foreign particles on the wafer 1, a photomultiplier, an avalanchephotodiode, a semiconductor photo-detector having an image intensifier,or the like is used as the light detector 9.

FIGS. 4A to 4B2 are to explain the angular ranges of scattered lightsdetected by multiple photodetectors according to the invention, or theplural detection optical units 102 a and 102 b. FIG. 4A is a diagramshowing an angular range in which each of the detection optical unitsdetects the scattered light. A hemisphere shown in FIG. 4A has an apexand an equatorial plane. The equatorial plane corresponds to the topsurface of the wafer 1. The apex is located in a direction that extendsfrom the center of the top surface of the wafer 1 and is parallel to thenormal to the top surface of the wafer 1. An azimuth (longitude) of anoptical axis of each of the detection optical units 102 is indicated byφ. The scanning direction S2 (direction of the translational movement ofthe translation stage 11) is used as a standard to define the azimuth φ.An angle formed between a line connecting the center of the equatorialplane with the apex and a line connecting the center of the equatorialplane with the center of an area R is indicated by θ. The area Rindicates the angular range in which each of the detection optical units102 detects the scattered light. The area R is located on thehemisphere. FIGS. 4B1 and 4B2 are diagrams each showing the equatorialplane when viewed from the apex of the hemisphere. In other words, eachof FIGS. 4B1 and 4B2 shows the equatorial plane drawn byparallel-projecting the hemisphere. In FIGS. 4B1 and 4B2, the angularranges in which the detection optical units 102 detect the scatteredlight are indicated by hatching. The plurality of detection opticalunits 102 is provided to cover a wide angular range and thereby capableof detecting a wide variety of defects. An angle at which light isscattered from a defect varies depending on the type and size of thedefect. The detection optical units 102 detect intensities of lightscattered at different angles. Signals indicating the detectedintensities of the light are processed by the signal processor 105(described later). Thus, the defect inspection apparatus is capable ofclassifying the types of various defects and estimating the sizes of thedefects with high accuracy.

FIG. 4B1 shows an example in which the defect inspection apparatusincludes detection optical units 102 suitable to inspect a foreignmaterial of several ten nanometers to several hundred nanometers. Lightscattered from an extremely small foreign material and directed at a lowangle (with respect to the equatorial plane) has a high intensity in thecase where P-polarized light is used for the illumination. Some of thedetection optical units 102 can detect an extremely small defect bydetecting, from almost all directions, light components scattered at lowangles (with respect to the equatorial plane). The other detectionoptical units 102 can detect a defect (dent) such as a crystaloriginated particle (COP) (from which light having a high intensity isscattered at a high angle) by detecting light components scattered at ahigh elevation angle with respect to the equatorial plane. FIG. 4B2shows an example in which the defect inspection apparatus includesdetection optical units 102 having large numerical apertures. In thecase where the detection optical units 102 has the large numericalapertures, the detection optical units 102 can detect scattered lighthaving a low intensity and are therefore suitable to detect an extremelysmall defect.

In both cases, the plurality of detection optical units 102 can detectlight scattered in a wide angular range. The detection optical units 102can detect light scattered from a defect in a direction that variesdepending on the type of the defect. Therefore, the detection opticalunits 102 can robustly detect a wide variety of defects. In addition,the detection optical units 102 detect light components scattered atelevation angles (low and high elevation angles) with respect to theequatorial plane. Thus, the detection optical units 102 can detect aconvex defect (such as a foreign material) and a concave defect (such asa COP and a scratch) and classify the defects.

Next, a description is made of the configuration of the illuminationintensity distribution control element 5 included in the illuminationoptical system 101 and a method for controlling an illuminationintensity distribution with reference to FIGS. 5A to 6C. FIG. 5A is adiagram showing the configuration of a part of the illumination opticalsystem 101 in the case where a transparent optical element is used asthe illumination intensity distribution control element 5. The lasersource 2 emits a laser beam 41. The laser beam 41 is adjusted by theillumination optical system 101 to ensure that the laser beam 41 has adesired intensity, desired polarization, and a desired beam diameter.The adjusted laser beam 41 then passes through the illuminationintensity distribution control element 5 and is introduced onto the topsurface of the wafer 1 via the focusing lens 6. The overall control unit53 is connected with a controller 14 (shown in FIG. 5A). The overallcontrol unit 53 transmits a signal to the controller 14. The controller14 receives the signal from the overall control unit 53 and controls theillumination intensity distribution control element 5 based on thereceived signal. FIG. 5B is a diagram showing the configuration of apart of the illumination optical system 101 in the case where areflective optical element is used as the illumination intensitydistribution control element 5. In addition, the optical element used asthe illumination intensity distribution control element 5 has a functionfor changing the intensity or phase of light that is to pass through theoptical element for each two-dimensional area (shown in FIG. 5C) or foreach one-dimensional area (shown in FIG. 5D). The function of theoptical element changes the intensity or phase of the light on a surfaceof the optical element that is perpendicular to an optical axis of theoptical element. An image formed on a light transmission surface or ofthe illumination intensity distribution control element 5 is projectedon the wafer 1 by the focusing lens 6. That is, the image projected onthe wafer 1 is similar to a distribution of intensities of lightmodulated by the illumination intensity distribution control element 5.A distance between the focusing lens 6 and a point at which the light isincident on the top surface of the wafer 1 and a distance between thefocusing lens 6 and the light transmission surface of the illuminationintensity distribution control element 5 are set to be the same as afocal length of the focusing lens 6. Thus, a Fourier transform image ofa light amplitude distribution, which is formed on the lighttransmission surface of the illumination intensity distribution controlelement 5, is projected on the wafer 1. Therefore, the illuminationintensity distribution provided by the illumination intensitydistribution control element 5 and corresponding to a transmittancedistribution and a phase distribution is formed on the wafer 1 by thefocusing lens 6. When a cylindrical lens is used as the focusing lens 6,the cylindrical lens transmits the light of the illumination intensitydistribution image in the direction of one of its optical axes andfocuses a laser beam (illumination light) in the direction of anotherone of the optical axes to allow the illumination intensity distribution(provided by the illumination intensity distribution control element 5and corresponding to the transmittance distribution or the phasedistribution) to be projected in the scanning direction S2 and allow anarea having a small length in the scanning direction S1 to beilluminated. A distribution of illumination intensities of the laserbeam emitted by the laser source 2 is represented by a substantialGaussian distribution. When the defect inspection apparatus does notcause the illumination intensity distribution control element 5 to act,the laser beam that exhibits a Gaussian distribution and is shaped bythe beam expander 7 and the focusing lens 6 is projected on the wafer 1.

As the illumination intensity distribution control element 5 having thefixed transmittance distribution or the fixed phase distribution, adiffractive optical element (DOE), a homogenizer (aspheric lens, microlens array, optical fiber bundle, or hollow pipe having an inner surfacecoated by reflective coating) or the like may be used. When theillumination intensity distribution control element 5 is composed of adynamically variable spatial light modulator (SLM) that is controlled bythe controller 14 connected with the overall control unit 53, the shapeof the illumination intensity distribution is dynamically controlled(adjusted) before and after the scanning of the illumination area 20 ofthe wafer 1 or during the scanning of the illumination area 20 of thewafer 1. The dynamically variable spatial light modulator oftransmission type is a liquid crystal element, a magneto-optical spatiallight modulator or the like. The dynamically variable spatial lightmodulator of reflection type is a digital micromirror device (DMD), agrating light valve (GLV), a reflection-type liquid crystal element(such as a liquid crystal on silicon (LCOS)) or the like.

FIGS. 6A to 6C are diagrams each showing an example of the illuminationintensity distribution formed by the illumination optical system 101having the aforementioned configuration. FIG. 6A shows a substantialGaussian distribution that indicates the distribution of theillumination intensities of the laser beam emitted by the laser source2. FIG. 6B shows a uniform illumination intensity distribution obtainedwhen the homogenizer or the like is used as the illumination intensitydistribution control element 5. The uniform illumination intensitydistribution shown in FIG. 6B is suitable to suppress thermal damage tothe wafer due to illumination with a laser beam having a high intensityand to maximize the amount of light scattered from a defect and therebyperform high-sensitivity inspection. FIG. 6C shows an illuminationintensity distribution dropped an intensity of a central portioncompared with the uniform illumination intensity distribution. Thetemperature rise generated when the uniform illumination intensitydistribution is formed becomes the maximum at a central portion of theillumination intensity distribution. Thus, thermal damage may occur atthe central portion of the illumination intensity distribution to thewafer. The illumination intensity distribution shown in FIG. 6C issuitable to avoid the thermal damage to the central portion of theillumination intensity distribution and detect the light with highsensitivity.

Next, the signal processor 105 according to the present invention isdescribed below. The signal processor 105 is adapted to classify varioustypes of defects and estimate the sizes of the defects based on signalsindicating the intensities of the light detected by the detectionoptical units (covering a wide angular range).

First, an analog processor 51 included in the signal processor 105 isdescribed below with reference to FIG. 7. The description below is madeof the analog processor 51 that is connected with the two detectionoptical units 102 a and 012 b for simplicity. The analog processor 51includes pre-amplifiers 501 a, 502 b, low pass filters 511 a, 511 b, andanalog-digital (A/D) converters 502 a, 502 b. The light detectors 9 aand 9 b output signal currents to the pre-amplifiers 501 a, 502 b,respectively. The signal currents output from the light detectors 9 aand 9 b are converted into voltages (analog signals) by thepre-amplifiers 501 a and 502 b, respectively. The pre-amplifiers 501 aand 502 b then amplify the voltages. The low pass filters 511 a, 511 bremove high frequency noise components from the amplified analogsignals. The A/D converters 511 a, 511 b has sampling rates sufficientlyhigher than cut-off frequencies of the low pass filters 511 a, 511 b.After the low pass filters 511 a, 511 b remove the high frequency noisecomponents, the A/D converters 511 a, 511 b convert the analog signalsinto digital signals and output the digital signals to a digitalprocessor 52, respectively.

Next, the digital processor 52 included in the signal processor 105 isdescried below with reference to FIG. 8. The signals output from theanalog processor 51 are received by high pass filters 604 a, 604 bincluded in the digital processor 52. The high pass filters 604 a, 604 bextract defect signals 603 a, 603 b from the received signals and outputthe defect signals 603 a, 603 b to a defect determination section 605included in the digital processor 52. The defect determination section605 receives the defect signals 603 a, 603 b. Since a defect is scannedin the illumination area 20 in the scanning direction S1, the waveformof each of the defect signals is obtained by enlarging or reducing anillumination intensity distribution profile (of the laser beam withwhich the area 20 is illuminated) in the scanning direction S1. The highpass filters 604 a, 604 b pass signals having frequencies within afrequency band that includes frequencies of the defect signals. The highpass filters 604 a, 604 b remove signals of a frequency band thatincludes a relatively large amount of noise and remove a direct currentcomponent that includes a relatively large amount of noise. Therefore,the high pass filters 604 a, 604 b improve the signal-to-noise ratios ofthe defect signals 603 a, 603 b, respectively. As the high pass filters604 a, 604 b, the following filters may be used: a high pass filterhaving a specified cut-off frequency and designed to shield a componenthaving a frequency equal to or higher than the cut-off frequency; a bandpass filter having a specified cut-off frequency and designed to shielda component having a frequency equal to or higher than the cut-offfrequency; a finite impulse response filter designed to pass a signalhaving a waveform similar to those of the defect signals. The defectdetermination section 605 performs threshold processing on the defectsignals output from the high pass filters 604 a, 604 b to determinewhether or not a defect is present. Specifically, the defectdetermination section 605 receives the defect signals that are based onthe signals detected by the detection optical units. The defectdetermination section 605 can perform threshold processing on the sum orweighted average of the defect signals, or perform OR logicalcalculation or AND logical calculation on a defect group extracted bythe threshold processing performed on the defect signals by means ofcoordinates set on the top surface of the wafer, to inspect the defectwith high sensitivity compared with defect inspection using a singledefect signal.

The defect determination section 605 calculates estimated positionalcoordinates (indicating the position of a defect on the wafer) and anestimated size of the defect based on the waveform of a defect signal(obtained from a location at which the defect is determined to bepresent) and a sensitivity information signal (obtained from thelocation at which the defect is determined to be present). The defectdetermination section 605 transmits, to the overall control unit 53, theestimated positional coordinates and the estimated size of the defect.The estimated positional coordinates and the estimated size of thedefect are transmitted as defect information 607. The estimatedpositional coordinates indicating the position of the defect iscalculated based on the barycenter of the waveform of the defect signal.The estimated size of the defect is calculated based on a value obtainedby integrating the waveform of the defect signal.

The signals output from the analog processor 51 are also received by lowpass filters 601 a, 601 b, respectively. The low pass filters 601 a, 601b are included in the digital processor 52. The low pass filters 601 a,601 b output, to a haze processor 606, low-frequency components anddirect current components, which correspond to the amount of light(haze) scattered from extremely small roughness present in theillumination area 20 on the wafer 1. The haze processor 606 receives thelow-frequency components and the direct current components and performsprocessing on the received components to obtain haze information. Thehaze processor 606 outputs a haze signal corresponding to the intensityof the haze for each location on the wafer based on the values of thesignals received from the low pass filters 601 a, 601 b. An angulardistribution of light scattered from the roughness of the wafer variesdepending on a spatial frequency distribution of extremely smallroughness. As shown in FIG. 8, haze signals are transmitted from thelight detectors 9 of the detection optical units 102 (located indifferent directions and at different angles with respect to the topsurface of the wafer) to the haze processor 606. Therefore, the hazeprocessor 606 can output information related to the spatial frequencydistribution of the extremely small roughness based on the ratio(s) ofthe intensities of the haze signals.

When a part of the laser beam reaches a convex part of the edge portionof the wafer, light is diffracted from the convex part. The diffractedlight has a high intensity. The diffracted light is incident on thelight detectors 9 of the detection optical units 102 that covers a largesolid angle. The light detectors 9 are therefore saturated. As a result,the defect inspection apparatus cannot perform the inspection. Inaddition, the light detectors 9 may be degraded or damaged since thelight detectors 9 receive a large amount of light. Light may bediffracted depending on the shape of a grip that holds the wafer at theedge portion of the wafer. In this case, the diffracted light has a highintensity.

According to the present invention, one or more of the detection opticalunit(s) 41 and the signal processor 105 as shown in FIG. 11 monitor theintensity of light diffracted from the edge portion of the wafer in theprocess for inspecting a defect present near the edge portion of thewafer. Only the light detector(s) of the detection optical unit(s) 41,to which the light diffracted from the edge portion propagates, is setto shield light. The light detectors 9 of the other detection opticalunits 102, which do not need to shield light, are set to detect lightfrom the top surface of the wafer (including a wafer portion locatednear the edge portion of the wafer) with high sensitivity. A failure(attachment of a foreign material, peeling of a film, or the like) mayeasily occur at the wafer portion located near the edge portion of thewafer. This configuration of the apparatus can maximize the total areaof a chip(s) that is included in the total area of the wafer and can beused as a good product(s). Therefore, the yield of the chip(s) isimproved. Next, the configuration of the defect inspection apparatus,which is a feature of the present invention, is described below withreference to the accompanying drawings.

First, a description is made of light diffracted from the edge portionof the wafer and light scattered from the edge portion of the wafer inthe case where the illumination area 20 according to the presentinvention is located near the edge portion of the wafer and scanned,with reference to FIGS. 9A and 9B. FIG. 9A shows the illumination area20 when viewed from a top side of the wafer. The illumination area 20 isscanned from the center of the top surface of the wafer 1 in thescanning directions S1 and S2. In FIG. 9A, the illumination area 20 ispresent near the edge portion of the wafer 1. FIG. 9B shows a crosssection of the wafer 1 in the case where the illumination area 20 ispresent near the edge portion of the wafer 1. The edge portion of thewafer 1 has inclination parts (upper and lower inclination parts) 31 anda side surface 32. Each of the upper and lower inclination parts 31 isgenerally called a bevel. The upper inclination part 31 is called anupper bevel herein. The side surface 32 is generally called an apex. Itis assumed that an illumination intensity distribution 21 of the laserbeam is a Gaussian distribution. The illumination intensity distribution21 is schematically illustrated in FIG. 9B. When an end portion (lowintensity part) of the illumination intensity distribution 21 is presentnear the edge portion of the wafer, light 22 is scattered and diffractedfrom the edge portion, especially from an angle portion of boundarybetween the upper bevel of the edge portion and the top surface of thewafer. The light 22 has a higher intensity than that of light scatteredfrom small roughness having a size of one nanometer to several angstromspresent on the top surface of the wafer. This is because a ruggednessscale of the angle portion of the bevel part boundary is extremely largemore than micron order (one micrometer to several micrometers) comparedwith the small roughness having a size of one nanometer to severalangstroms. Thus, the ruggedness scale is significantly larger than thesmall roughness. An angular distribution of the light scattered anddiffracted from the edge portion is schematically illustrated in FIG.9C. FIGS. 9A to 9C are drawn based on the method for illustratingazimuths and angles that are used for the detection optical unitdescribed with reference to FIG. 4A. The line of the boundary betweenthe upper bevel of the edge portion and the top surface of the wafer isperpendicular to the direction of propagation of the illumination light(laser beam) due to the spiral scanning performed by means of thescanning in the circumferential direction S1 and the scanning in thetranslational direction S2. Therefore, light 24 is diffracted from theedge portion in the direction of incidence of the illumination light onthe top surface of the wafer, in the direction 23 of propagation oflight specularly reflected and in the direction toward the apex of thehemisphere, as shown in FIG. 9C. Light 25 is scattered around thediffracted light 24 due to the boundary between the upper bevel of theedge portion and the top surface of the wafer and due to roughness ofthe bevel as shown in FIG. 9C.

When the diffracted light 24 is directly incident on the light detector9 of the detection optical unit 102, the light detector 9 may bedegraded or damaged. This is because the diffracted light 24 has a highintensity.

A method for avoiding the degradation and damage of the light detector9, which is a feature of the present invention, is described below withreference to FIGS. 10A to 11.

First, a system (composed of the detection optical unit(s) 41 and thesignal processor 105) for monitoring the intensity of the lightdiffracted from the edge portion of the wafer is described below withreference to FIGS. 10A to 10C. The detection optical units 102 arearranged in the same manner as the arrangement described with referenceto FIG. 4B1. As shown in FIG. 10A, the light 24 diffracted from the edgeportion is incident on some of the detection optical units. Thedetection optical units that receive the diffracted light 24 arehereinafter denoted by reference numeral 41. As a result, the lightdetectors 9 of the detection optical units 41 detect signals,respectively. The detected signals passes through the analog processor51 and are received by the low pass filters 601 included in the digitalprocessor 52. Then, the low pass filters 601 output diffracted lightintensity signals (each of which indicates the intensity of the lightdiffracted from the edge portion) shown in FIGS. 10B and 10C. FIG. 10Bshows the case where the illumination intensity distribution of theillumination light (laser beam) is a Gaussian distribution, while FIG.10C shows the case where the illumination intensity distribution of theillumination light (laser beam) is uniform (and includes a rapidreduction in the illumination intensity at a location distant from thecenter of a spot of the laser beam incident on the top surface of thewafer). Since the illumination intensity distribution shown in FIG. 10Bis a Gaussian distribution, the intensity of the diffracted lightintensity signal shown in FIG. 10B increases as the illumination area 20approaches the edge portion of the wafer 1. On the other hand, since theillumination intensity distribution shown in FIG. 10C is uniform, theintensity of the diffracted light intensity signal shown in FIG. 10Crapidly increases as the illumination area 20 approaches the edgeportion of the wafer. The speed of the scanning in the translationaldirection S2 (radial direction of the wafer) is lower than the speed ofthe scanning in the circumferential direction S2. Thus, the intensity ofthe diffracted light intensity signal (shown in FIG. 10C) graduallychanges with respect to time. For example, the haze processor 606 canmonitor the diffracted light intensity signals by monitoring hazesignals output from the detection optical units 41, i.e., by monitoringsignals output from the low pass filters 601. Thus, the haze processor606 determines whether or not the intensity of the haze signal outputfrom each of the detection optical units 41 is higher than apredetermined threshold for triggering shielding of light, for example.When the intensity of the haze signal output from the detection opticalunit 41 is higher than the predetermined threshold, a light shieldingunit (shown in FIG. 11 and described later) shields the light diffractedfrom the edge portion and having a high intensity to prevent the lightfrom being incident on the light detectors 9 of the detection opticalunits 102. This can prevent the light detectors 9 from being damaged dueto the light diffracted from the edge portion.

In the uniform illumination intensity distribution (of the illuminationlight) shown in FIG. 10C, an illumination intensity at a locationdistant from the center of the spot of the laser beam incident on thetop surface of the wafer is lower than that in the Gaussian distribution(indicated by an alternate long and short dash line shown in FIG. 10C).Thus, the light diffracted from the edge portion and the light scatteredfrom the edge portion have low intensities in a region Re that islocated near the edge portion. Therefore, when the illuminationintensity distribution of the illumination light is uniform,high-sensitivity inspection can be performed on the region Re in asimilar manner as the inspection performed on the top surface of thewafer.

The light shielding unit (light blocking unit) included in the detectionoptical unit 41 is described below with reference to FIG. 11. Thedetection optical unit 41 is configured by adding a light shieldingshutter (light blocking shutter) 15 to the configuration of thedetection optical unit 120. A light shielding shutter controller 16transmits an electrical switch signal to the light shielding shutter 15based on a diffracted light intensity signal monitored by the digitalprocessor 52 and determined that the signal has an intensity higher thanthe predetermined threshold for triggering shielding of light. The lightshielding shutter 15 is switched to a light shielding state or to alight transmission state based on the electrical switch signal receivedfrom the light shielding shutter controller 16. When the light shieldingshutter 15 is switched to the light shielding state, the light shieldingshutter 15 shields the laser beam. When the light shielding shutter 15is switched to the light transmission state, the light shielding shutter15 transmits the laser beam. As the light shielding shutter 15, amechanical shutter, a liquid crystal filter, an electrooptical element,an acoustooptic element or the like may be used. The light shieldingshutter controller 16 receives, from the digital processor 52, adetermination signal indicating whether or not the intensity of thelight diffracted from the edge portion is higher than a certainintensity value. When the intensity of the light diffracted from theedge portion is higher than the certain intensity value, the lightshielding shutter controller 16 transmits, to the light shieldingshutter 15, a signal instructing the light shielding shutter 15 to beset to the light shielding state. Only the detection optical unit(s) 41having the aforementioned configuration(s) can shield the light toprotect the light detector(s) 9. Each of the detection optical unit(s)41 would receive an excessive amount of the light diffracted from theedge portion if the detection optical unit 41 did not have the lightshielding shutter 15.

Next, an edge grip according to the present invention is described belowwith reference to FIGS. 12A to 12D. The edge grip is adapted to hold thewafer. An edge chuck is used to press the edge portion from the oppositeside of the wafer and thereby hold the wafer in order to prevent a backsurface of the wafer from being contaminated and prevent a foreignmaterial from being attached to the back surface of the wafer. A part ofthe edge chuck, which contacts and holds the edge portion of the wafer,is called the edge grip. The edge grip is denoted by reference numeral81. FIG. 12A shows the edge grip 81 when viewed from a top side of theedge grip 81. FIG. 12A also schematically illustrates a cross section ofthe edge grip 81. The edge grip 81 has a side (ridge) extending in adirection substantially parallel to the scanning direction S1, i.e., thecircumferential direction of the wafer. This side of the edge grip 81 isindicated by a bold line shown in FIG. 12A. The side of the edge grip 81is regarded as an edge grip ridge 83. The edge grip 81 also has a side(ridge) extending in a direction substantially parallel to the scanningdirection S2, i.e., the radial direction of the wafer. This side of theedge grip 81 is regarded as an edge grip ridge 82. An angle formedbetween the top surface of the wafer and a surface (on which theillumination light is incident) of the edge grip, i.e., an angle formedbetween the top surface of the wafer and the edge grip ridge 82, isindicated by φe. As shown in FIG. 12A, a portion of the edge grip 81 islocated on the side of a central portion of the wafer with respect tothe apex 32. Thus, light diffracted and scattered from the edge grip 81may disturb high-sensitivity inspection on a wafer portion located nearthe edge portion.

When the illumination area 20 is present near the edge portion of thewafer, light is diffracted and scattered from the edge grip 81 in asimilar manner to the light diffracted and scattered from the edgeportion. In the case where the surface (on which part of theillumination light is incident) of the edge grip 81 and the edge gripridges 82, 83 are ground to reduce irregularities, intensities of lightscattered from the edge grip 81 are lower than those of light diffractedfrom the edge grip 81. Thus, light 85 and 86 diffracted from the edgegrips 82, 83 is dominant among light generated from the edge grip 81.FIG. 12B illustrates directions of propagation of the light 85, 86diffracted from the edge grip ridges 82, 83 based on of the method(described with reference to FIG. 4A) for illustrating azimuths andangles that are used for the detection optical unit. The edge grip ridge83 extends in the same direction as that of extension of the boundarybetween the bevel of the edge portion and the top surface of the waferof the bevel. Thus, the light 86 diffracted from the edge grip ridge 83propagates in the direction of the incidence of the illumination light,in the direction 23′ of the propagation of the light specularlyreflected on the surface of the edge grip, and in the direction towardthe apex of the hemisphere. On the other hand, the edge grip ridge 82extends in a direction perpendicular to the direction of extension ofthe edge grip ridge 83. Thus, the light 85 diffracted from the edge gripridge 82 propagates through the path of the propagation of thespecularly reflected light and in a direction perpendicular to thedirection of the propagation of the light 86 diffracted from the edgegrip ridge 83. A distance between the center of the top surface of thewafer and an edge of the wafer is regarded as 1. This distance means adistance between the apex of the hemisphere and a point crossing thefollowing two lines: a line that is parallel to the top surface of thewafer and extends from the apex of the hemisphere; and a line that isparallel to the normal to the top surface of the wafer and extends fromthe edge of the wafer. The following distance is indicated by k: adistance between the apex of the hemisphere and a point crossing thedirection 23′ of the propagation of the light specularly reflected onthe surface of the edge grip 81 and the line that is parallel to the topsurface of the wafer and extends from the apex of the hemisphere. Thedirection of the propagation of the light 85 diffracted from the edgegrip ridge 82 is determined by the distance k. The distance k iscalculation by the following formula. When the angle of the incidence ofthe illumination light on the surface of the edge grip 81 with respectto the normal to the top surface of the wafer is indicated by φi, anangle at which the light specularly reflected on the surface of the edgegrip is indicated by a value of (φi−2φe). In accordance with thedefinition shown in FIG. 4A, k=sin(φi−2φe). Therefore, the distance k,which determines the direction of the diffracted light 85, can beselected based on the shape (e.g., the angle φe or the like) of the edgegrip 81 and the incident angle φi of the illumination light.

FIG. 12C shows the case where the distance k is set to a distance k1that minimizes the number of the detection optical units receiving thelight diffracted from the edge grip ridges. As shown in FIG. 12C, thediffracted light 85 is incident on only a detection optical unit 87. Thedetection optical unit 87 receives the light 24 (shown in FIG. 9C)diffracted from the edge portion and the light 85 (shown in FIG. 12B)diffracted from the edge grip ridge 82 (The detection optical units 41include the detection optical unit 87). The detection optical units 41selectively shield (block) the light diffracted from the edge portionand the edge grip by means of the light shielding units shown in FIGS.10A to 11 to prevent the light detectors 9 of the detection opticalunits 41 from being damaged. In this case, the other detection opticalunits 102 are capable of detecting a defect.

FIG. 12D shows the case where the distance k is set to a distance k2that prevents the diffracted light 85 from being incident on any of thedetection optical units. In the case shown in FIG. 12D, it is effectiveto increase the incident angle φi of the illumination light (i.e., toperform illumination at a low elevation angle) and reduce the angle φe(i.e., to set the surface (on which the illumination light is incident)of the edge grip to be nearly parallel to the top surface of the wafer).In order to prevent the diffracted light 85 from being incident on anyof the detection optical units, it is necessary that the distance k2 be,for example, larger than 0.95. In order to set the distance k2 to belarger than 0.95, it is necessary that the value of (φi−2φe) be largerthan 72 degrees. Thus, it is necessary to use an edge grip satisfyingthe following requirements: when φi=70 degrees, φe<−1 degree; and whenφi=80 degrees, φe<4 degrees. The incident angle φi of the illuminationlight may be set based on the shape of the edge grip 81.

As described above, the defect inspection apparatus is capable ofpreventing the light detectors of the detection optical units 41 frombeing damaged and of detecting, with high sensitivity, a defect presentin a wide area that includes a wafer portion located near the edgeportion and a wafer portion located near the edge grip. Thus, the defectinspection apparatus is capable of maximizing the total area of achip(s) that is included in the total area of the wafer and can be usedas a good product(s) to improve the yield of the product(s).

Next, a description is made of an analyzer (polarizing filter) forremoving the light 24 diffracted from a wafer portion located near theedge portion of the wafer and incident on a detection optical unit 41and the light 86 diffracted from the edge grip 81 (that presses the edgeportion of the wafer to hold the wafer) and incident on any of thedetection optical units 41 (including the detection optical unit 87)with reference to FIG. 13.

In order to detect an extremely small defect present on small roughnessof the wafer, the illumination optical system 101 illuminates the wafer1 with a P-polarized laser beam from a direction oblique to the normalto the top surface of the wafer 1. An electric field is generated by theillumination with the P-polarized light from the oblique direction. Aplane including the incident direction of the illumination light and thedirection of the normal to the top surface of the wafer is regarded asan incident plane of the illumination light. The electric fieldoscillates only in a direction parallel to the incident plane. Thus, thelight diffracted and scattered in the incident plane oscillates in thedirection (left-right direction of FIG. 13A) parallel to the incidentplane. When each of the detection optical units 41 (including thedetection optical unit 87) uses a polarizing filter capable of shieldinglight having a polarization direction parallel to the incident plane,the detection optical units 41 (including the detection optical unit 87)can shield the diffracted light 24 and the diffracted light 86.

In order to detect a defect present on relatively coarse roughness ofthe wafer, the illumination optical system 101 shown in FIG. 1 uses anS-polarized laser beam as the illumination light to illuminate theroughness with the S-polarized laser beam from a direction oblique tothe normal to the top surface of the wafer. In the case where the waferis illuminated with the S-polarized laser beam, the polarizationdirection (top-bottom direction of FIG. 13B) of the light 24 diffractedfrom the edge portion of the wafer and the polarization direction(top-bottom direction of FIG. 13B) of the light 86 diffracted from theedge grip 81 are perpendicular to the polarization direction of thelight 24 diffracted from the edge portion due to the illumination withthe P-polarized laser beam from the oblique direction and to thepolarization direction of the light 86 diffracted from the edge grip 81due to the illumination with the P-polarized laser beam from the obliquedirection. When the detection optical unit 41 uses a polarizing filter13 capable of shielding light having the polarization direction(parallel to that of light 24, 86 diffracted due to the illuminationwith the S-polarized laser beam), the detection optical unit 41 canshield the light 24 diffracted from the edge portion of the wafer due tothe illumination with the S-polarized laser beam and the light 86diffracted from the edge grip 81 due to the illumination with theS-polarized laser beam.

As described above, each of the detection optical units 41 (includingthe detection optical unit 87) has the polarizing filter (analyzer) 13to detect an extremely small defect present on fine roughness of thewafer and detect a defect present on relatively coarse roughness of thewafer. The polarizing filter (analyzer) 13 is set in a crossed nicolsstate with respect to the polarization of the illumination light.Accordingly, each of the detection optical units 41 (including thedetection optical unit 87) can selectively shield (block) the light 24diffracted from the edge portion and the light 86 diffracted from theedge grip 81. In this case, after light scattered from a defect passesthrough the polarizing filter 13, each of the detection optical units 41(including the detection optical unit 87) detects the light scatteredfrom the defect. This is because the polarization state of the lightscattered from the defect is disturbed depending on the shape andmaterial of the defect. Each of the other detection optical units doesnot include the analyzer (polarizing filter) 13. Thus, each of the otherdetection optical units can detect a defect in a wide area extendingfrom a wafer portion located near the edge portion to a wafer portionlocated near the edge grip.

Next, a description is made of a unit (wafer cross sectional profilemeasurement unit) for measuring displacement of an illumination area anda unit for correcting the position of the illumination area withreference to FIGS. 14 and 15. These two units are used to correct theposition of the illumination area displaced due to displacement(displacement of an inclination angle of the top surface anddisplacement of the vertical position of the top surface of the wafer)of the top surface of the wafer. The two units prevent the illuminationarea from being present outside a field of view of the detection opticalunit and prevent the inspection sensitivity to be reduced. FIG. 14 is adiagram showing the outline configuration of the illumination areadisplacement measurement unit (wafer cross sectional profile measurementunit) according to the present invention. FIG. 15 is a diagram showingthe outline configuration of the illumination area position correctionunit according to the present invention. An angle of the direction ofpropagation of the illumination light specularly reflected on the topsurface of the wafer with respect to the normal to the top surface ofthe wafer and the position of a wafer portion on which the illuminationlight is specularly reflected vary depending on the inclination angle ofthe top surface of the wafer and on the vertical position of the topsurface of the wafer. The illumination area displacement measurementunit (wafer cross sectional profile measurement unit) has a focusinglens 203, a position detector 204, a half mirror 201, a positiondetector 202 and a processing circuit 205. The focusing lens 203 has afocal length f as shown in FIG. 14. The focusing lens 203 is located onan optical path of the illumination light specularly reflected. Also,the focusing lens 203 is separated from the top surface of the wafer bya distance sufficiently larger than the focal length f. The positiondetector 204 is located to ensure that a distance between a detectionsurface of the position detector 204 and the focusing lens 203 is equalto the focal length f. The position detector 204 is adapted to detect,as positional displacement, displacement of the angle at which the lightis specularly reflected on the top surface of the wafer with respect tothe normal to the top surface of the wafer due to displacement of theinclination angle of the top surface of the wafer and due todisplacement of the vertical position of the top surface of the wafer.The position detector 202 is located on an optical path of the lightspecularly reflected and deflected by the half mirror 201. The positiondetector 202 is adapted to detect displacement of the angle at which thelight is specularly reflected on the top surface of the wafer withrespect to the normal to the top surface of the wafer and displacement(i.e., displacement of the illumination area 20) of the location atwhich the light is specularly reflected on the top surface of the wafer.The processing circuit 205 performs processing to subtract thedisplacement (detected by the position detector 204) of the angle atwhich the light is specularly reflected on the top surface of the waferwith respect to the normal to the top surface of the wafer from thedisplacement (detected by the position detector 202) of the angle atwhich the light is specularly reflected on the top surface of the waferwith respect to the normal to the top surface of the wafer and thedisplacement of the illumination area 20 to calculate the displacementof the illumination area 20. The processing circuit 205 transmits asignal indicating the displacement of the illumination area 20 to theoverall control unit 53. The overall control unit 53 receives the signalfrom the processor circuit 205 and divides the displacement of theillumination area 20 by sin(φi) to convert the displacement of theillumination area 20 into displacement of the vertical position of thetop surface of the wafer. The overall control unit 53 stores thedisplacement of the vertical position of the top surface of the waferfor each scanned region R defined in the scanning direction(translational direction) S2 to obtain the profile of the cross sectionof an wafer portion extending from the top surface to the edge portion.The profile obtained by the overall control unit 53 is displayed by thedisplay unit 54 as a graph.

When the illumination area 20 is displaced due to displacement of thevertical position of the top surface of the wafer and thereby presentoutside the field of view of any of the detection optical units, theinspection sensitivity is reduced. To avoid this, it is necessary tocorrect the position of the illumination area by means of theillumination area position correction unit based on the displacement(measured by the illumination area displacement measurement unit (wafercross section profile measurement unit)) of the illumination area 20.The illumination area position correction unit included in theillumination optical system 101 has a beam deflecting element 211, afocusing lens 212 and a mirror 213(m 2) on an optical path of theillumination optical system 101. The beam deflecting element 211controls the direction of the propagation of the illumination light.Then, the illumination light is reflected on the mirror 213(m 2) andintroduced onto the wafer 1. An illumination area position correctioncontroller 214 controls the beam deflecting element 211 to adjust thedegree of the deflection of the illumination light and thereby adjustthe direction of the propagation of the illumination light. In addition,the illumination area position correction controller 214 controls thebeam deflecting element 211 based on the measured displacement(transmitted from the processing circuit 205 (including the overallcontrol unit 53)) of the illumination area 20 to place the illuminationarea 20 at its original location. Thus, the position of the illuminationarea 20 with respect to an angular range in which scattered light isdetected by each of the detection optical units is corrected for thedisplacement of the inclination angle of the top surface of the wafer(including a wafer portion located near the edge portion) and thedisplacement of the vertical position of the top surface of the wafer(including a wafer portion located near the edge portion). That is, theangle of the direction of the propagation of the specularly reflectedlight with respect to the normal to the top surface of the wafer and thelocation at which the light is specularly reflected (for example, thedirection 23 of propagation of light specularly reflected and thedirection 23′ of the propagation of the light specularly reflected onthe surface of the edge grip 81) are corrected for the displacement ofthe inclination angle of the top surface of the wafer (including a waferportion located near the edge portion) and the displacement of thevertical position of the top surface of the wafer (including a waferportion located near the edge portion). As a result, the detectionoptical unit(s) 41 (including the detection optical unit 87) shields(blocks) the light 24 diffracted from the edge portion and the light 86diffracted from the edge grip 81, while the other detection opticalunits do not receive the diffracted light 24, 86 and detect lightscattered in a wide angular range to inspect the top surface of thewafer and a wafer portion located near the edge portion of the waferwith high sensitivity.

According to the embodiment of the present invention, the defectinspection apparatus has the wafer cross sectional profile measurementunit and the illumination area position correction unit to correctdisplacement of the illumination area due to displacement (displacementof the inclination angle and the displacement of the vertical position)of the top surface of the wafer, i.e., due to displacement of the angleat which the illumination light is specularly reflected on the topsurface of the wafer with respect to the normal to the top surface ofthe wafer, and displacement of the position of the wafer portion onwhich the illumination light is specularly reflected (for example, thedirection 23 and the direction 23′). The specified detection opticalunit (s) shields (blocks) the light diffracted from the edge portion andthe light diffracted from the edge grip, while the other detectionoptical units can cover a wide angular range by means of the lightdetectors and increase the inspection sensitivity by setting focaldepths to be small and increasing spatial resolutions. According to theembodiment of the present invention, the illumination optical system 101scans the wafer with an extremely laser beam spot, and the plurality ofdetection optical units 102 detects light scattered at a large solidangle with a high efficiency of converging light. Therefore, the defectinspection apparatus is capable of inspecting the top surface of thewafer and detecting a defect of several hundred nanometers to severalten nanometers from a wafer portion located near the edge portion of thewafer to perform high-sensitivity inspection.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description and all changeswhich come within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

1. An apparatus for inspecting defects, comprising: an illuminationoptical system for guiding light emitted by a light source onto a sampleto illuminate a particular area of the sample as an illumination area; aplurality of detection optical units for converging from a plurality ofdirections light generated from the sample when illuminated by theillumination optical system to obtain detection signals of the light ona direction-by-direction basis; and a signal processor for processing aplurality of detection signals obtained by the plurality of detectionoptical units to judge whether or not a defect is present on the sample;wherein upon inspection of a near-edge portion of the sample, in adetection optical unit, of the plurality of detection optical units, onwhich diffracted light generated from the near edge portion is incident,the incident diffracted light is blocked by diffracted light blockingmeans in accordance with a signal obtained by monitoring the intensityof the incident diffracted light.
 2. The apparatus for inspectingdefects according to claim 1, wherein upon inspection of a near edgeportion of the sample, the signal processor processes a signal obtainedby a detection optical unit, of the plurality of detection opticalunits, on which the diffracted light generated from the near edgeportion of the sample is not incident to judge whether or not a defectis present on the sample.
 3. The apparatus for inspecting defectsaccording to claim 1, further comprising: positional-displacementmeasurement means for measuring a positional displacement of theillumination area on the wafer, wherein the illumination optical systemincludes means for correcting the position of the illumination area onthe sample based on the positional displacement measured by thepositional-displacement measurement means.
 4. An apparatus forinspecting defects, comprising: an illumination optical system forguiding light emitted by a light source onto a sample to illuminate aparticular area of the sample as an illumination area; a plurality ofdetection optical units for converging from a plurality of directionslight generated from the sample when illuminated by the illuminationoptical system to obtain detection signals of the light on adirection-by-direction basis; and a signal processor for processing aplurality of detection signals obtained by the plurality of detectionoptical units to judge whether or not a defect is present on the sample;wherein upon inspection of a near edge grip portion of the sample, in adetection optical unit, of the plurality of detection optical units, onwhich diffracted light generated from an edge grip portion is incident,the incident diffracted light is blocked by diffracted light blockingmeans in accordance with a signal obtained by monitoring the intensityof the incident diffracted light.
 5. The apparatus for inspectingdefects according to claim 4, wherein upon inspection of a near edgegrip portion of the sample, the signal processor processes a signalobtained by a detection optical unit, of the plurality of detectionoptical units, on which the diffracted light generated from an edge gripportion is not incident to judge whether or not a defect is present onthe sample.
 6. The apparatus for inspecting defects according to claim4, further comprising: positional-displacement measurement means formeasuring a positional displacement of the illumination area on thewafer, wherein the illumination optical system includes means forcorrecting the position of the illumination area on the sample based onthe positional displacement measured by the positional-displacementmeasurement means.
 7. An apparatus for inspecting defects, comprising:an illumination optical system for guiding light emitted by a lightsource onto a sample to illuminate a particular area of the sample as anillumination area; a plurality of detection optical units for convergingfrom a plurality of directions light generated from the sample whenilluminated by the illumination optical system to obtain detectionsignals of the light on a direction-by-direction basis; and a signalprocessor for processing a plurality of detection signals obtained bythe plurality of detection optical units to judge whether or not adefect is present on the sample; wherein upon inspection of a near edgeportion and a near edge grip portion of the sample, in a detectionoptical unit, of the plurality of detection optical units, on which isincident either diffracted light generated from the near edge portion ordiffracted light generated from an edge grip portion, the diffractedlight incident on the detection optical unit is blocked by diffractedlight blocking means in accordance with a signal obtained by monitoringthe intensity of the incident diffracted light.
 8. The apparatus forinspecting defects according to claim 7, wherein upon inspection of anear edge portion and a near edge grip portion of the sample, the signalprocessor processes a signal obtained by a detection optical unit, ofthe plurality of detection optical units, on which is not incident thediffracted light generated from the near edge portion and an edge gripportion to judge whether or not a defect is present on the sample. 9.The apparatus for inspecting defects according to claim 7, furthercomprising: positional-displacement measurement means for measuring apositional displacement of the illumination area on the wafer, whereinthe illumination optical system includes means for correcting theposition of the illumination area on the sample based on the positionaldisplacement measured by the positional-displacement measurement means.10. An apparatus for inspecting defects, comprising: an illuminationoptical system for guiding light emitted by a light source onto a sampleto illuminate a particular area of the sample with polarized light; aplurality of detection optical units for converging from a plurality ofdirections light generated from the sample when illuminated with thepolarized light by the illumination optical system to obtain detectionsignals of the light on a direction-by-direction basis; and a signalprocessor for processing a plurality of detection signals obtained bythe plurality of detection optical units to judge whether or not adefect is present on the sample; wherein upon inspection of a near edgeportion and a near edge grip portion of the sample, in a detectionoptical unit, of the plurality of detection optical units, on which isincident either diffracted light generated from the near edge portion ordiffracted light generated from an edge grip portion, the polarizationcomponents of the diffracted light incident on the detection opticalunit are blocked by a polarizing filter.
 11. The apparatus forinspecting defects according to claim 10, wherein upon inspection of anear edge portion and a near edge grip portion of the sample, the signalprocessor processes a signal obtained by a detection optical unit, ofthe plurality of detection optical units, on which is not incident thediffracted light generated from the near edge portion and an edge gripportion to judge whether or not a defect is present on the sample.
 12. Amethod for inspecting defects, comprising the steps of: guiding lightemitted by a light source onto a sample to illuminate a particular areaof the sample; converging scattered light generated from the sampleilluminated the light from a plurality of directions and detecting thescattered light on a direction-by-direction basis with each detectionoptical unit; and processing a plurality of detection signals detectedon the direction-by-direction basis with the each detection optical unitto judge whether or not a defect is present on the sample; wherein uponinspection of a near edge portion of the sample, a detection signal, ofthe plurality of detection signals, that represents diffracted lightgenerated from a near edge portion of the sample or from an edge gripportion that holds the sample or from both is used in the process ofblocking the diffracted light or blocking the main polarizationcomponents of the diffracted light with the use of a polarizationfilter.
 13. A method for inspecting defects, comprising the steps of:guiding light emitted by a light source onto a sample to illuminate aparticular area of the sample; detecting scattered light generated fromthe illuminated area of the sample with a plurality of detection opticalunits, the directions of which is different from one another; andprocessing a plurality of detection signals obtained by the plurality ofdetection optical units to judge whether or not a defect is present onthe sample; wherein upon inspection of a near edge portion of thesample, whether or not a defect is present on the sample is judged usinga detection signal that is output from an detection optical unit whichdiffracted light generated from the near edge portion and/or from anedge grip portion that holds the sample does not enter.